Generation of Fluorescent Adducts of Malondialdehyde and Amino Acids: Toward an Understanding of Lipofuscin¶

Post-Translational Modifications Evoked by Reactive Carbonyl Species in Ultraviolet-A-Exposed Skin: Implication in Fibroblast Senescence and Skin Photoaging

Photoaging is an accelerated form of aging resulting from skin exposure to ultraviolet (UV) radiation. UV-A radiation deeply penetrates the dermis and triggers the generation of reactive oxygen species (ROS) which promotes damage to DNA, lipids and proteins. Lipid peroxidation results from the oxidative attack of polyunsaturated fatty acids which generate a huge amount of lipid peroxidation products, among them reactive carbonyl species (RCS) such as α, β-unsaturated hydroxyalkenals (e.g., 4-hydroxynonenal), acrolein or malondialdehyde. These highly reactive agents form adducts on free NH2 groups and thiol residues on amino acids in proteins and can also modify DNA and phospholipids. The accumulation of RCS-adducts leads to carbonyl stress characterized by progressive cellular and tissular dysfunction, inflammation and toxicity. RCS-adducts are formed in the dermis of skin exposed to UV-A radiation. Several RCS targets have been identified in the dermis, such as collagen and elastin in the extracellular matrix, whose modification could contribute to actinic elastosis lesions. RCS-adducts may play a role in fibroblast senescence via the modification of histones, and the sirtuin SIRT1, leading to an accumulation of acetylated proteins. The cytoskeleton protein vimentin is modified by RCS, which could impair fibroblast motility. A better identification of protein modification and carbonyl stress in the dermis may help to develop new treatment approaches for preventing photoaging.

Chemistry and biochemistry of lipid peroxidation products

Oxidative stress and resulting lipid peroxidation is involved in various and numerous pathological states including inflammation, atherosclerosis, neurodegenerative diseases and cancer. This review is focused on recent advances concerning the formation, metabolism and reactivity towards macromolecules of lipid peroxidation breakdown products, some of which being considered as 'second messengers' of oxidative stress. This review relates also new advances regarding apoptosis induction, survival/proliferation processes and autophagy regulated by 4-hydroxynonenal, a major product of omega-6 fatty acid peroxidation, in relationship with detoxication mechanisms. The use of these lipid peroxidation products as oxidative stress/lipid peroxidation biomarkers is also addressed.

Fluorescence spectroscopy of the retina for diagnosis of transmissible spongiform encephalopathies

The feasibility of exploiting fluorescence spectra of the eye for diagnosis of transmissible spongiform encephalopathies (TSEs) was examined. Retinas from scrapie-positive sheep were compared with scrapie-negative sheep using fluorescence spectroscopy, and distinct differences in the fluorescence intensity and spectroscopic signatures were observed. The characteristic fluorescent signatures are thought to be the result of an accumulation of lipofuscin in the retina. It appears that the eye, in particular the retina, is a useful tissue for noninvasive examination of some neurological pathologies such as scrapie. The development of procedures based on examinations of the eye that permit the detection of neurological disorders in animals holds great promise.

Fluorescence-based method, exploiting lipofuscin, for real-time detection of central nervous system tissues on bovine carcasses

The removal of central nervous system (CNS) tissues as part of bovine spongiform encephalopathy (BSE) risk material is one of the highest priority tasks to avoid contamination of the human food chain with BSE. No currently available method enables the real-time detection of possible CNS tissue contamination on carcasses during slaughter. The fluorescent pigment lipofuscin is a heterogeneous, high-molecular weight material that has been shown to be enriched in high concentrations in neuronal tissues. In this study, lipofuscin fluorescence was investigated as a marker for real-time detection of CNS contamination. Front-faced fluorescence spectra of brain and spinal cord samples from 11 cattle gave identical, reproducible fluorescence signal patterns with high intensities. The specificity of these spectra was assessed by investigating 13 different non-CNS tissues enabling the differentiation of brain and spinal cord by signal intensity and structure of the spectra, respectively. Small quantities of bovine spinal cord were reliably detected in the presence of raw bovine skeletal muscle, fat, and vertebrae. The presented data are a fundamental basis for the development of a prototype device allowing real-time monitoring of CNS tissue contamination on bovine carcasses and meat cuts.

You say lipofuscin, we say ceroid: defining autofluorescent storage material

Accumulation of intracellular autofluorescent material or "aging pigment" has been characterized as a normal aging event. Certain diseases also exhibit a similar accumulation of intracellular autofluorescent material. However, autofluorescent storage material associated with aging and disease has distinct characteristics. Lipofuscin is a common term for aging pigments, whereas ceroid is used to describe pathologically derived storage material, for example, in the neuronal ceroid lipofuscinoses (NCLs). NCLs are a family of neurodegenerative diseases that are characterized by an accumulation of autofluorescent storage material (ceroid) in the lysosome, which has been termed "lipofuscin-like". There have been many studies that describe this autofluorescent storage material, but what is it? Is this accumulation lipofuscin or ceroid? In this review we will try to answer the following questions: (1) What is lipofuscin and ceroid? (2) What contributes to the accumulation of this storage material in one or the other? (3) Does this material have an effect on cellular function? Studying parallels between the accumulation of lipofuscin and ceroid may provide insight into the biological relevance of these phenomena.

Phospholipid transfer protein (PLTP) deficiency reduces brain vitamin E content and increases anxiety in mice

Vitamin E supplementation constitutes a promising strategy in the prevention of neurodegenerative diseases. Here, we show that a phospholipid transfer protein (PLTP) is widely expressed in the brain where it appears to function as a transfer factor for alpha-tocopherol, the main isomer of vitamin E. PLTP deficiency results in significant depletion of brain alpha-tocopherol in both homozygous (-30.1%, P<0.0002) and heterozygous (-18.0%, P<0.05) PLTP knocked-out mice. Alpha-tocopherol depletion in PLTP-deficient homozygotes is associated with the elevation of lipofuscin (+25% and +450% increases in cortex and substantia nigra, respectively), cholesterol oxides (+54.5%, P<0.05), and cellular peroxides (+32.3%, P<0.01) in the brain. Complete PLTP deficiency in homozygotes is accompanied by increased anxiety as shown by fewer entries (8.3% vs. 44.4% in controls, P<0.01) and less time spent (1.7% vs. 41.3% in controls, P<0.05) in the open arms of an elevated plus-maze, in the absence of locomotor deterioration. Thus, the vitamin E transfer activity of PLTP appears to be a key process in preventing oxidative damage in the brain, and PLTP-deficient mice could be a new model of the contribution of oxidative brain injury in the etiology of neurodegenerative diseases.